Transesterification using trimethanolethane in the presence of triethylamine affords the corresponding crystalline phosphite (eq 1).Triethyl phosphite has been used extensively in the synthesis of phosphonates via the Arbuzov reaction., This general protocol works well with a variety of electrophiles and is carried out by simply heating the reactants between 100 °C and 150 °C using phosphite as solvent.
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Phosphonates bearing electron withdrawing groups to phosphorus represent a valuable class of reagents which have been creatively applied to the stereoselective synthesis of alkenes (eqs 2-6). Acyl phosphonates, prepared from the corresponding acid halides, have been utilized as intermediates in the overall reduction of acids to aldehydes (eq 7), and as intermediates in the preparation of vinylphosphonates (eq 8).A nonclassical Arbuzov approach to -methoxybenzylphosphonates employs the treatment of acetals of aromatic aldehydes with triethyl phosphite in the presence of (eq 9). In contrast, direct arene phosphorylation has been achieved through treatment of aromatic substrates with triethyl phosphite and . In this case the active species is believed to be a phosphite radical cation (eq 10).
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For example, reaction of di--butyl disulfide with triethyl phosphite in the presence of carbon monoxide gives a nearly quantitative yield of the corresponding homologated thioester (eq 26).In a completely unrelated example, [2,2]paracyclophane was synthesized from the corresponding bis-thioether via photochemical extrusion of sulfur mediated by triethyl phosphite (eq 27). The concept of linking proximal carbon atoms with the extrusion of sulfur was used successfully by Eschenmoser in his synthesis of a vitamin B intermediate (eq 28), while a modification of Barton's method allowed the synthesis of the highly strained diquadricyclanylidene (eq 29).A bimolecular coupling mediated by triethyl phosphite was applied to the synthesis of an interesting unsymmetrical tetrathiafulvalene, although yields were low due to competing homo coupling (eq 30).Triethyl phosphite reacts with -diketones to form isolable cyclic phosphate esters.
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Hydroperoxides, for example, are rapidly converted to alcohols after treatment with one equivalent of the reagent at ambient temperature (eq 14). The reduction of peroxides generated in situ via enolate oxidation is a powerful technique for achieving regio and stereoselective -hydroxylation (eq 15). In addition to reducing hydroperoxides, triethyl phosphite has been utilized for the deoxygenation of -peroxides (eq 16), diaroyl peroxides (eq 17) and the reductive coupling of phthalic anhydride (eq 18).Scott reported that terminal epoxides can be reduced using forcing conditions while internal epoxides are generally unaffected, even at temperatures approaching 200 °C. In contrast, Saegusa and co-workers discovered that -keto acids are easily reduced to -hydroxy acids under mild conditions in good to excellent yields (eq 19).The deoxygenation of nitrogenous functionalities using triethyl phosphite has also received attention. Reductive cyclization of aromatic nitro-containing compounds has provided entry into a variety of heterocycles (eqs 20 and 21). It has been suggested that a highly reactive nitrene intermediate is involved in the cyclization process. Aryl nitroso compounds subjected to these conditions experience a similar fate, although the reactive intermediate in this case is believed to be polar in nature (eq 22).Azides are also subject to reduction by triethyl phosphite via a modified Staudinger process (eq 23).A frequently encountered application of triethyl phosphite is the conversion of cyclic thiocarbonates to the corresponding alkenes (Corey-Winter synthesis). The reaction proceeds stereospecifically via a carbene intermediate and often results in good yields of desired alkene (eqs 24 and 25).The conversion of thiiranes to alkenes proceeds readily, in contrast to epoxide reduction. For example, the episulfides of - and -2-butene are reduced smoothly and with high stereospecificity.